I. Technical Field
The present invention relates to a shaft seal packing enhanced in shaft seal performance and to a shaft seal structure for a valve, such as a ball valve or gate valve, organically enhanced in seal performance at dynamic and static parts of a shaft seal section of the valve and in slidability at the dynamic part.
II. Description of the Related Art
Conventionally, for example, a ball valve comprises a valve disc, such as a ball valve disc, for controlling a fluid and a stem for operating the valve disc and, since the rotation of the stem makes an opening/closing operation, the stem has a rotation part required to have a seal mechanism. The seal mechanism of the stem rotation part requires the frictional force exerted by the rotation of the stem to be reduced and is required to have a function of maintaining the sealability with the stem or a body. Also, in an ascending/descending valve, such as a gate valve, it is necessary to reduce the frictional force exerted during ascending and descending and similarly maintain the sealability. To satisfy these, for a seal at a stem-mounted part a molded packing made of a resin (fluorine resins, such as PTFE) is generally used.
The packing is formed of a resin into a V-shape in cross section and attached to the inside of a valve in a stacked manner to add to a tightening force and enhance the sealability. In addition, the packing has a structure to fulfill a sealing force called self-sealability that automatically performs tight stoppage when a fluid has acted on the stem and the inner wall of the body.
As the valve using the V-shaped packing, a ball valve described in JP-A HEI 10-231823 can be cited. The ball valve has a substantially cylindrical V-shaped packing attached between a stem and a body. Similarly to the ball valve of JP-A HEI 10-231823, a ball valve 1 shown in FIG. 18 has a general structure using a V-shaped packing made of a resin, such as PTFE.
In this ball valve 1, the pressing force of a stem part 4 in the axial direction obtained through tightening a bolt-nut assembly 2 presses a gland 9 to press an annular packing 3 disposed at a lower side via the gland 9. The annular packing 3 converts, at a mountain-shaped tapered face part 3a V-shaped in cross section, the axial-direction pressing force into a radial-direction pressing force to heighten surface pressure relative to the stem part 4 or a sidewall 5a of a packing storage chamber 5, thereby attaining a sealing effect. In addition, a fluid is guided to the annular packing 3 and received at a valley-shaped tapered face part 3b V-shaped in cross section to push the annular packing 3 radially and heighten the surface pressure relative to the stem part 4 or sidewall 5a owing to the fluid pressure, thereby attaining the sealing effect by self-sealability.
To be specific, in FIG. 19(a), the annular packing having a mountain-side taper angle α of 47.5° formed from the normal of the mountain-shaped tapered face part 3a and a valley-side taper angle β of 45° formed from the normal of the valley-shaped tapered face part 3b, for example, is attached between an upper adapter 6 having a valley-shaped tapered face part 6a of the same angle as mentioned above and a lower adapter 7 having a mountain-shaped tapered face part 7a of the same angle as mentioned above to constitute a stacked ring 8. By means of each angle difference of 2.5°, gaps S are formed on the inner-diameter and outer-diameter sides at an initial time of pressing the stacked ring 8, with the apexes as their centers, between the upper adapter 6 and the annular packing 3 and between the lower adapter 7 and the packing 3.
In the annular packing 3 and upper adapter 6, edge parts 3b1 and 6a1 on the inner and outer peripheral sides of the respective valley-shaped tapered face parts 3b and 6a come into contact with the mountain-shaped tapered face parts 3a and 7a, respectively, of the annular packing 3 and lower adapter 6 disposed on the lower side in the drawing and, when the bolt-nut assembly 2 has been tightened, the edge parts 3b1 and 6a1 are pressed toward the sides of the stem part 3 and packing storage chamber 5, respectively, to form contact seals.
Also, in FIG. 19(b), when retightening the bolt-nut assembly 2 shown in FIG. 18, the mountain-shaped tapered face parts 3a and 7a and the valley-shaped tapered face parts 3b and 6a of the stacked ring 8 are urged to come into intimate contact with each other over the entire surfaces thereof. At this time, the edge parts 3b1 and 6a1 on the inner and outer peripheral sides of the valley-shaped tapered face parts 3b and 6a are deformed as projecting slightly toward the inner-diameter and outer-diameter sides, respectively, and parts thus deformed are pressed against and brought into intimate contact with the stem part 4 and packing storage chamber 5. Thus, the retightening of the bolt-nut assembly enables the sealability to be enhanced.
In the meantime, in FIG. 19(c), when a fluid flows within the ball valve 1, the fluid pressure received by the ball valve produces a force acting to lift the lower adapter 7. Though this force is exerted in the axial direction, the tapered face parts 3a, 3b, 6a and 7a of the stacked ring 8 convert the force to loads in the diametrical direction (on the inner-diameter and outer-diameter sides). As a result, the stacked ring 8 is pressed against the outer peripheral surface of the stem part 4 and packing storage chamber 5 to form seals. Thus, the stacked ring 8 on which the fluid pressure has been exerted exercise its self-sealability to form seals.
In the upper adapter 6, annular packing 3 and lower adapter 7 constituting the stacked ring 8, since the mountain-side taper angle α and valley-side taper angle β are equal on the outer-diameter and inner-diameter sides, the mountain-shaped taper face parts 3a and 7a and valley-shaped taper face parts 3b and 6a when receiving the fluid pressure are uniformly deformed symmetrically from the center sections to narrow the gaps S in the stacked ring 8. At this time, the stacked ring 8 is deformed as pushed radially to bring the distal end sections thereof on the inner-diameter and outer-diameter sides to a contact seal state relative to the outer peripheral surface of the stem part 4 and packing storage chamber 5. That is to say, the contact seal is formed by means of a so-called lip effect (sealing effect by line contact).    Patent Document 1: